One option is to use the input panel as a confirmation dialog. Insert "Y" or "N". I have done this myself in my HexViewer plugin (before sublime ever added okay_cancel dialogs; you could also use the quick panel and popup up the snooze option in the list or cancel). Or you could just allow a command to snooze it. The user can bind the snooze command to a shortcut or access it from the menu or command palette. In the latter case of just having a snooze command, there would be no dialog, the user would just need to execute the snooze command (this would be in the documentation).

That's a shame, the OK / Cancel is perfect as it flashes the task bar if you've not got ST in view and it's impossible to ignore (accidentally or otherwise) if you have it in view. Never mind, it'll have to be an option for ST2 users

Updated with a tiny local wav file for the alarm now as it was just the easiest way all around + everything works as it should.

It uses afplay on OSX, aplay on Linux (requires ALSA) and a tiny (4KB) exe on windows (source code included) to play the alarm file. If anyone is on OSX and can test I'd be really grateful: https://github.com/CodeEffect/AlarmClock

Also, if this setup doesn't work for anyone (no alsa, OSX older than 10.5 etc etc) could they let me know and if at all possible advise an alternative please?